Lecture - Week 1 and 2 Development: Difference between revisions
No edit summary |
|||
(136 intermediate revisions by 4 users not shown) | |||
Line 1: | Line 1: | ||
[[ | {{Header}} | ||
[[Week 1]] | [[Week 2]] | [[Zygote]] | [[Morula]] | [[Blastocyst]] | [[Implantation]] | |||
==Introduction== | |||
[[File:Week1_summary.jpg|thumb|450px|Week 1 and 2 Development (see [[Week 1 Movie]])]] | |||
This lecture will discuss the first two weeks of human embryogenesis and describe the cleavage stages, blastocyst formation and hatching, and the generation of the bilaminar embryo. There will also be an introduction to the uterine changes at implantation, that will be covered in detail in the placentation lecture. | |||
==Objectives== | ==Objectives== | ||
* Understand the events during week 1 of development (Zygote, Blastomeres, Morula, Blastocyst) | * Understand the events during week 1 of development (Zygote, Blastomeres, Morula, Blastocyst) | ||
* Understand the events during week 2 of development (Trophoblast, Syncytiotrophoblast, Cytotrophoblast, Embryoblast, Implantation) | * Understand the events during week 2 of development (Trophoblast, Syncytiotrophoblast, Cytotrophoblast, Embryoblast, Implantation) | ||
Line 8: | Line 14: | ||
* Brief understanding of maternal changes | * Brief understanding of maternal changes | ||
==Lecture Resources== | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Movies | |||
|- | |||
| valign="bottom"|{{Human blastocyst movie 1}} | |||
| valign="bottom"|{{Human blastocyst movie 2}} | |||
| valign="bottom"|{{Human blastocyst movie 3}} | |||
|- | |||
| valign="bottom"|{{Mouse zygote movie}} | |||
| valign="bottom"|{{Mouse zygote movie 1}} | |||
| valign="bottom"|{{Mouse zygote movie 2}} | |||
| valign="bottom"|{{Mouse Blastocyst movie}} | |||
|- | |||
| valign="bottom"|{{Morula model movie}} | |||
| valign="bottom"|{{Blastocyst model movie}} | |||
|- | |||
! Week 2 | |||
|- | |||
| valign="bottom"|{{Week 2 implant movie}} | |||
| valign="bottom"|{{Week 2 bilaminar movie}} | |||
| valign="bottom"|{{Embryo 1.6mm movie 1}} | |||
|} | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! References | |||
|- | |||
| {{Embryo logocitation}} | |||
| | |||
* [https://embryology.med.unsw.edu.au/embryology/index.php?title=Lecture_-_Week_1_and_2_Development&oldid=296205 2017] | [[Media:2015ANAT2341 Lecture 3 - Week 1 and 2 Development.pdf|2015 Lecture PDF]] | |||
* [[Menstrual Cycle|Menstrual Cycle]] | [[Week 1]] | [[Week 2]] | [[Implantation]] | |||
* Lecture Archive: [https://embryology.med.unsw.edu.au/embryology/index.php?title=Lecture_-_Week_1_and_2_Development&oldid=211101 2015] | [[Media:2015ANAT2341 Lecture 3 - Week 1 and 2 Development.pdf|2015 PDF]] | [[Media:ANAT2341 Lecture 3 - 2014 Week 1 and 2 Development.pdf|2014 PDF]] | [[Media:ANAT2341_Lecture_2_-_Beverdam_-_Week_1_and_2.pdf|2013 PDF]] | [http://embryology.med.unsw.edu.au/embryology/index.php?title=Lecture_-_Week_1_and_2_Development&oldid=97577 2012] | [http://embryology.med.unsw.edu.au/embryology/index.php?title=Lecture_-_Week_1_and_2_Development&oldid=61429 2011] | [[2010_Lecture_3|2010]] | [[2009_Lecture_3|2009]] | [[2010_Lecture_3|2010]] | |||
|- | |||
| {{MPT2015cover_citation}} | |||
| The following chapter links only work with a UNSW connection. | |||
* [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=34 First Week of Human Development] | |||
* [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=65 Second Week of Human Development]|- | |||
| {{SBBFP2015cover_citation}} | |||
| The following chapter links only work with a UNSW connection. | |||
* [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074524&ppg=32 Gametogenesis, Fertilization, and First Week] | |||
* [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074524&ppg=61 Second Week: Becoming Bilaminar and Fully Implanting] | |||
|} | |||
Take the [[Week 1 and 2 Quiz]] (this is '''not''' the 2018 assessment quiz that will be held in the practical class). | |||
==Fertilization== | |||
[[File:ova20he.jpg|thumb|alt=Antral Follicle and Oocyte|Antral Follicle and Oocyte]] | |||
[[File:Intracytoplasmic_sperm_insemination.jpg|thumb|alt=Intracytoplasmic sperm insemination|Intracytoplasmic sperm insemination ([[Assisted_Reproductive_Technology|ART]])]] | |||
{| | |||
| | |||
* Fertilization usually occurs in first 1/3 of oviduct. | |||
* Fertilization can also occur outside oviduct, associated with In Vitro Fertilization (IVF, GIFT, ZIFT...) and ectopic pregnancy. | |||
* The majority of fertilized eggs do not go on to form an embryo. | |||
| | |||
{{Fertilization movie 2}} | |||
|} | |||
===Fertilization - Spermatozoa === | |||
* '''Sperm Binding''' - zona pellucida protein ZP3 acts as receptor for sperm | |||
* '''Acrosome Reaction''' - exyocytosis of acrosome contents (Calcium mediated) [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3741 MBoC - Figure 20-31. The acrosome reaction that occurs when a mammalian sperm fertilizes an egg] | |||
** enzymes to digest the zona pellucida, exposes sperm surface proteins to bind ZP2 | |||
* '''Membrane Fusion''' - between spermatozoa and oocyte, allows spermatozoa nuclei passage into oocyte cytoplasm | |||
[[File:Model of gamete recognition zona pellucida.jpg|500px]] | |||
===Fertilization- Oocyte=== | |||
* '''Membrane Depolarization''' - caused by sperm membrane fusion, primary block to polyspermy | |||
* '''Cortical Reaction''' - IP3 pathway elevates intracellular Calcium, exocytosis of cortical granules [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3743 MBoC - Figure 20-32. How the cortical reaction in a mouse egg is thought to prevent additional sperm from entering the egg] | |||
** enzyme alters ZP3 so it will no longer bind sperm plasma membrane | |||
* '''Meiosis 2''' - completion of 2nd meiotic division | |||
** forms second polar body (a third polar body may be formed by meiotic division of the first polar body) | |||
== Zygote Formation== | == Zygote Formation== | ||
* zygote is the first diploid cell formed following fertilisation. | * zygote ([[Carnegie stage 1]]) is the first diploid cell formed following fertilisation. | ||
* male and female pronuclei, 2 nuclei approach each other and nuclear membranes break down. | * male and female pronuclei, 2 nuclei approach each other and nuclear membranes break down. | ||
* DNA replicates, first mitotic division | * DNA replicates, first mitotic division | ||
* sperm contributes centriole which organizes mitotic spindle | * sperm contributes centriole which organizes mitotic spindle | ||
{| | {| | ||
| [[File:Stage1_size_with_ruler.jpg|200px]] | |||
| [[File:Human_zygote_two_pronuclei_22.jpg|300px]] | | [[File:Human_zygote_two_pronuclei_22.jpg|300px]] | ||
| [[File:Parental_genome_mix_01_icon.jpg| | | [[File:Parental_genome_mix_01_icon.jpg|200px]] | ||
|} | |} | ||
[[Development_Animation_-_Pronuclear_Fusion|Movie - Pronuclear Fusion]] | [[Movie_-_Parental_genomes|Movie - Parental Genomes]] | {| class="wikitable mw-collapsible mw-collapsed" | ||
! Pronuclear Fusion and Parental Genomes Movies | |||
|- | |||
| <html5media height="340" width="320">File:Pronuclear_fusion_001.mp4</html5media> | |||
[[Media:Pronuclear_fusion_001.mp4|'''Click Here''' to play on mobile device]] | |||
[[Development_Animation_-_Pronuclear_Fusion|Movie - Pronuclear Fusion]] | |||
| <html5media height="340" width="320">File:Parental_genome_mix_02.mp4</html5media> | |||
[[Media:Parental_genome_mix_02.mp4|'''Click Here''' to play on mobile device]] | |||
[[Movie_-_Parental_genomes|Movie - Parental Genomes]] | |||
|} | |||
:'''''Conceptus''' - the term refers to all material derived from this fertilised zygote, includes both the embryo and the non-embryonic tissues (placenta, fetal membranes).'' | :'''''Conceptus''' - the term refers to all material derived from this fertilised zygote, includes both the embryo and the non-embryonic tissues (placenta, fetal membranes).'' | ||
:'''Links:''' [[Carnegie stage 1]] | :'''Links:''' [[Fertilization]] | [[Carnegie stage 1]] | ||
==Cleavage of Zygote== | ==Cleavage of Zygote== | ||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Zygote Division Movie | |||
|- | |||
| <html5media height="400" width="400">File:Mouse_zygote_division.mp4</html5media> | |||
[[Media:Mouse_zygote_division.mp4|'''Click Here''' to play on mobile device]] | [[Mouse_Zygote_1_Movie|Mouse Zygote Movie page]] | |||
|} | |||
{| | |||
| | |||
* cleavage of zygote forms 2 blastomeres and is also cleavage with no cytoplasm synthesis. | * cleavage of zygote forms 2 blastomeres and is also cleavage with no cytoplasm synthesis. | ||
** special "embryonic" cell cycle '''S''' phases and '''M''' phases alternate without any intervening '''G1''' or '''G2''' phases (MSMSMSMS, adult MG1SG2) therefore individual cell volume decreases. | ** special "embryonic" cell cycle '''S''' phases and '''M''' phases alternate without any intervening '''G1''' or '''G2''' phases (MSMSMSMS, adult MG1SG2) therefore individual cell volume decreases. | ||
* cell division is initially synchronous, then asynchronously | * cell division is initially synchronous, then asynchronously | ||
* | * cell division becomes slower (centre cells, larger) and faster in peripheral cells | ||
* zona pellucid still intact (division occurs within the ZP) | * zona pellucid still intact (division occurs within the ZP) | ||
| [[Image:Cell_cycle1.jpg|400px]] | |||
|} | |||
[[File:Human blastocyst day 1-6.jpg]] | |||
Human Zygote to Blastocyst Development (day 1 to 6) | |||
:'''Links:''' [[Carnegie stage 2]] | | |||
== Morula == | == Morula == | ||
{| border='0px' | {| border='0px' | ||
|- | |- | ||
Line 54: | Line 163: | ||
** outer cell layer - '''trophoblast''', peripheral flattened cells, forms the placenta and placental membranes | ** outer cell layer - '''trophoblast''', peripheral flattened cells, forms the placenta and placental membranes | ||
** inner cell mass - '''embryoblast''', mass of rounder cells located on one wall of the blastocoel, forms entire embryo | ** inner cell mass - '''embryoblast''', mass of rounder cells located on one wall of the blastocoel, forms entire embryo | ||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Human Blastocyst Movies | |||
|- | |||
| <html5media height="470" width="500">File:Human_blastocyst_day_3-6.mp4</html5media> | |||
[[Media:Human_blastocyst_day_3-6.mp4|'''Click Here''' to play on mobile device]] | |||
|} | |||
===Blastula Cell Communication=== | ===Blastula Cell Communication=== | ||
Two forms of cellular junctions | Two forms of cellular junctions | ||
*''' tight junctions''', close to outer surface create a seal, isolates interior of embryo from external medium | |||
* '''gap junctions''', allow electrically couple cells of epithelium surrounding a fluid-filled cavity | * '''gap junctions''', allow electrically couple cells of epithelium surrounding a fluid-filled cavity | ||
{| | |||
| [[File:Tight_junction_01.jpg|300px]] | |||
| [[File:Gap junction 01.jpg|300px]] | |||
|- | |||
| Tight junctions | |||
| Gap junctions | |||
|} | |||
===Blastocyst Hatching=== | ===Blastocyst Hatching=== | ||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Human Blastocyst Hatching Movie | |||
|- | |||
| <html5media height="470" width="500">File:Human_blastocyst_hatching_day_5-6.mp4</html5media> | |||
[[Media:Human_blastocyst_hatching_day_5-6.mp4|'''Click Here''' to play on mobile device]] | [[Blastocyst_Hatching_Movie|Movie page]] | |||
|} | |||
[[ | [[File:Human_carnegie_stage_3_label.jpg|400px|Hatching Blastocyst]] | ||
'''Blastocyst Hatching''' - zona pellucida lost, ZP has sperm entry site, and entire ZP broken down by uterine secretions and possibly blastula secretions. | '''Blastocyst Hatching''' - zona pellucida lost, ZP has sperm entry site, and entire ZP broken down by uterine secretions and possibly blastula secretions. | ||
'''Uterine Glands''' - secretions required for blastocyst motility and nutrition | '''Uterine Glands''' - secretions required for blastocyst motility and nutrition | ||
[[File:Human_blastocyst_day_1-6.jpg|600px]] | |||
Line 71: | Line 204: | ||
== Week 2 - Implantation == | == Week 2 - Implantation == | ||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Implantation Movie | |||
|- | |||
| width=520px|<html5media height="580" width="500">File:Week2_001.mp4</html5media> | |||
[[Media:Week2_001.mp4|'''Click Here''' to play on mobile device]] | [[Implantation_Movie|Movie page]] | |||
|} | |||
The second week of human development is concerned with the process of implantation and the differentiation of the blastocyst into early embryonic and placental forming structures. | The second week of human development is concerned with the process of implantation and the differentiation of the blastocyst into early embryonic and placental forming structures. | ||
{| | {| | ||
Line 82: | Line 222: | ||
'''Normal Implantation Sites''' - in uterine wall superior, posterior, lateral | '''Normal Implantation Sites''' - in uterine wall superior, posterior, lateral | ||
| | | | ||
| valign="bottom"|{{Week 2 implant movie}} | |||
|} | |||
[[File:Stage5 bf11L.jpg|alt=Human embryo Carnegie stage 5|400px]] | |||
[[File:Stage5 bf08.jpg|alt=Human embryo Carnegie stage 5|380px]] | |||
===Endometrial Receptivity=== | ===Endometrial Receptivity=== | ||
{| | |||
| | |||
* In humans, receptivity occurs 6 days after the post-ovulatory progesterone surge and lasts about 2 to 4 days. | * In humans, receptivity occurs 6 days after the post-ovulatory progesterone surge and lasts about 2 to 4 days. | ||
** Similar "receptivity window" in other species (rat day 5 and mouse day 4.5). | ** Similar "receptivity window" in other species (rat day 5 and mouse day 4.5). | ||
* Many studies have looked into identifying markers for this receptivity period both to optimise and to block this process. | * Many studies have looked into identifying markers for this receptivity period both to optimise and to block this process. | ||
| [[File:Implantation_LIF.jpg|400px]] | |||
|} | |||
===Abnormal Implantation=== | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Ectopic Ultrasound Movie | |||
|- | |||
| <html5media height="550" width="660">File:Ectopic_01.mp4</html5media> | |||
[[Media:Ectopic_01.mp4|'''Click Here''' to play on mobile device]] | |||
|} | |||
[[Image:Tubal pregnancy.gif|thumb|Ectopic tubal pregnancy]] | [[Image:Tubal pregnancy.gif|thumb|Ectopic tubal pregnancy]] | ||
Line 109: | Line 263: | ||
:'''Links:''' [[ | :'''Links:''' [[Implantation]] | [[Abnormal_Development_-_Ectopic_Implantation|Ectopic Pregnancy]] | [[Ultrasound_-_Ectopic_01|Movie - Ectopic pregnancy ultrasound]] | ||
== Uterus == | |||
{| | |||
| | |||
[[File:Menstrual cycle.png|400px|Menstrual cycle]] | |||
* Endometrium - 3 layers in secretory phase of menstrual cycle: compact, spongy, basal | |||
* Myometrium - muscular layer outside endometrium, contracts in parturition | |||
* Perimetrium - tunica serosa of the uterus continuous with the peritoneal wall | |||
| [[File:Uterus proliferative phase.jpg]] | |||
|} | |||
<gallery> | |||
Uterus proliferative phase.jpg|Uterus proliferative phase | |||
Uterine gland proliferative phase.jpg|Uterine gland proliferative phase | |||
Uterus secretory phase.jpg|Uterus secretory phase | |||
Uterine gland secretory phase.jpg|Uterine gland secretory phase | |||
</gallery> | |||
===Endometrial Layers=== | |||
* Compact - implantation occurs in this layer, dense stromal cells, uterine gland necks, capillaries of spiral arteries | |||
* Spongy - swollen stromal cells, uterine gland bodies, spiral arteries | |||
* Basal - not lost during menstruation or childbirth, own blood supply | |||
===Decidual Reaction=== | |||
[[File:Placenta anchoring villi.jpg|thumb|Decidual Reaction]] | |||
* transformation of endometrial stromal cells | |||
* occurs initially at site of implantation and includes both cellular and matrix changes | |||
* reaction spreads throughout entire uterus, not at cervix | |||
* deposition of fibrinoid and glycogen and epithelial plaque formation (at anchoring villi) | |||
* presence of decidual cells are indicative of pregnancy | |||
[[File:Bailey494.jpg|thumb|300px]] | |||
===Other Uterine Changes=== | |||
* '''Cervix''' - at mouth of uterus, secretes mucus (CMP), forms a plug/barrier, mechanical and antibacterial | |||
* '''Vascular''' - increased number of blood vessels | |||
===Decidua=== | |||
The endometrium becomes the decidua and forms 3 distinct anatomical regions (at approx 3 weeks) | |||
* Decidua Basalis at implantation site | |||
* Decidua Capsularis enclosing the conceptus | |||
* Decidua Parietalis the remainder of uterus | |||
** Decidua Capsularis and Parietalis fuse eventually fuse and uterine cavity is lost by 12 weeks | |||
=== Uterus Abnormalities === | |||
'''Endometriosis''' endometrial tissue located in other regions of the uterus or other tissues. This misplaced tissue develops into growths or lesions which respond to the menstrual cycle hormonal changes in the same way that the tissue of the uterine lining does; each month the tissue builds up, breaks down, and sheds. | |||
== Conceptus== | |||
===Bilaminar Embryoblast === | |||
{| | |||
| | |||
* about '''day 8 to 9''' | |||
* The outer trophoblast and inner embryoblast layers now both differentiate to form two distinct cellular layers. | |||
* The trophoblast layer forms the '''syncitotrophoblast''' and '''cytotrophoblast''' layers. | |||
* The embryoblast (inner cell mass) forms the '''epiblast''' and '''hypoblast''' layers. | |||
** '''Epiblast''' - will form the 3 germ layers. | |||
** '''Hypoblast''' - transient layer replaced by endoderm. | |||
* This early stage of embryo development is referred to as the '''bilaminar embryo'''. | |||
| <html5media height="300" width="250">File:Chorion 001.mp4</html5media> | |||
[[Development_Animation_-_Chorionic_Cavity|Movie - Week 2 Bilaminar Embryo]] | |||
|} | |||
===Bilaminar Trophoblast=== | |||
Two trophoblast layers Cytotrophoblast and Syncitiotrophoblast. | |||
'''Cytotrophoblasts''' - form a continuous cellular layer that covers the developing placental villi. | |||
'''Syncitiotrophoblasts''' | |||
* '''secrete proteolytic enzymes''', enzymes break down extracellular matrix around cells | |||
* Allow passage of blastocyst into endometrial wall, totally surround the blastocyst | |||
* generate spaces that fill with maternal blood- lacunae | |||
* '''secrete Human Chorionic Gonadotropin''' (hCG), hormone, maintains decidua and Corpus Luteum, basis of pregnancy diagnostic test, present in urine is diagnostic of pregnancy | |||
** levels peak at 8 to 10 weeks of pregnancy, then decline and are lower for rest of pregnancy | |||
** 1-2 months: 5,000-200,000 mIU/ml; Non-pregnant females: <5.0 mIU/ml; Postmenopausal females: <9.5 mIU/ml) | |||
** Later in development placenta will secrete hCG | |||
{| | |||
| [[File:Human ovary - corpus luteum 21.jpg|250px]] | |||
| [[File:Trophoblast_cell_hCG.jpg|250px]] | |||
| [[File:Pregnancy test.gif|250px]] | |||
|- | |||
| Human ovary corpus luteum | |||
| Trophoblast hCG | |||
| Pregnancy Test Kit | |||
|} | |||
[[Image:Ovary_corpus_luteum.jpg|300px|Ovary corpus luteum]] | |||
== Twinning == | |||
Twinning can be due to two separate fertilization events (dizygotic twins) or as an abnormality of a single fertilization (monozygotic twins) event during the early weeks of development. | |||
===Dizygotic Twinning=== | |||
Dizygotic twins (fraternal, non-identical) arise from separate [[F#fertilization|fertilization]] events involving two separate [[O#oocyte|oocyte]] (egg, ova) and [[S#spermatozoa|spermatozoa]] (sperm). | |||
* In '''dizygotic twinning''' the genetic material is different and implantation and placentation is also different. | |||
===Monozygotic Twinning=== | |||
* In '''monozygotic twinning''' the genetic material is initially identical and degree of twinning will depend upon the timing (early to late) from separate fetal membranes and placenta to conjoined twins. | |||
** morula stage (diamniotic dichorionic), early blastocyst (diamniotic monochorionic), late blastocyst to bilaminar (monoamniotic monochorionic), bilaminar to trilaminar embryo (conjoined) | |||
* Monozygotic twins are a unique research resource for comparing environmental effects on development and health. | |||
* Congenital abnormality statistics for twins is generally increased in various conditions. | |||
Monoygotic twins (identical) produced from a single [[F#fertilization|fertilization]] event (one fertilised egg and a single spermatazoa, form a single zygote), these twins therefore share the same genetic makeup. Occurs in approximately 3-5 per 1000 pregnancies, more commonly with aged mothers. The later the twinning event, the less common are initially separate placental membranes and finally resulting in conjoined twins. | |||
{| class="prettytable" 100% | |||
| width=10% | '''Week''' | |||
| | |||
| colspan="7" | Week 1 | |||
| colspan="7" | Week 2 | |||
|-bgcolor="lightsteelblue" | |||
| '''Day''' | |||
| width=5% | 0 | |||
| width=5% | 1 | |||
| width=5% | 2 | |||
| width=5% | 3 | |||
| width=5% | 4 | |||
| width=5% | 5 | |||
| width=5% | 6 | |||
| width=5% | 7 | |||
| width=5% | 8 | |||
| width=5% | 9 | |||
| width=5% | 10 | |||
| width=5% | 11 | |||
| width=5% | 12 | |||
| width=5% | 13 | |||
| width=5% | 14 | |||
|- | |||
| '''Cell Number''' | |||
| 1 | |||
| 1 | |||
| 2 | |||
| 16 | |||
| 32 | |||
| 128 | |||
| | |||
| | |||
| | |||
| bilaminar | |||
| | |||
| | |||
| | |||
| | |||
| | |||
|- | |||
| '''Event''' | |||
| Ovulation | |||
| fertilization | |||
| First cell division | |||
| Morula | |||
| Early blastocyst | |||
| Late blastocyst | |||
Hatching | |||
| Implantation starts | |||
| | |||
| | |||
| [[Molecular_Development_-_X_Inactivation|X inactivation]] | |||
| | |||
| | |||
| | |||
| | |||
| | |||
|- | |||
| | |||
| [[File:Follicle 001 icon.jpg|50px]] | |||
| [[File:Early_zygote.jpg|50px]] | |||
| [[File:Human embryo day 2.jpg|50px]] | |||
| [[File:Human embryo day 3.jpg|50px]] | |||
| [[File:Human embryo day 5.jpg|50px]] | |||
| [[File:CSt3.jpg|50px]] | |||
| [[File:Week2_001 icon.jpg|50px]] | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
|-bgcolor="lightsteelblue" | |||
| '''Monoygotic''' | |||
'''Twin Type''' | |||
| | |||
| colspan="3" | Diamniotic | |||
Dichorionic | |||
| colspan="3" | Diamniotic | |||
Monochorionic | |||
| colspan="3" | Monoamniotic | |||
Monochorionic | |||
| colspan="5" | Conjoined | |||
|- | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
| | |||
|} | |||
Table based upon recent Twinning Review.<ref><pubmed>12957099</pubmed></ref> | |||
<references/> | |||
:'''Links:''' [[Abnormal_Development_-_Twinning| Twinning]] | [http://www.twins.org.au/index.php?page=31 Australian Twin Registry] | |||
Now watch the [[Week 1 Movie|Week 1 overview]]. | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! Week 1 Movie | |||
|- | |||
| <html5media height="260" width="660">File:Week1_001.mp4</html5media> | |||
[[Media:Week1_001.mp4|'''Click Here''' to play on mobile device]] | |||
|} | |||
{{2018ANAT2341}} | |||
[[Category:Science-Undergraduate]] | |||
[[Category:Week 1]] [[Category:Week 2]] | [[Category:Week 1]] [[Category:Week 2]] |
Latest revision as of 15:45, 24 September 2019
Embryology - 16 Jun 2024 Expand to Translate |
---|
Google Translate - select your language from the list shown below (this will open a new external page) |
العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt These external translations are automated and may not be accurate. (More? About Translations) |
Week 1 | Week 2 | Zygote | Morula | Blastocyst | Implantation
Introduction
This lecture will discuss the first two weeks of human embryogenesis and describe the cleavage stages, blastocyst formation and hatching, and the generation of the bilaminar embryo. There will also be an introduction to the uterine changes at implantation, that will be covered in detail in the placentation lecture.
Objectives
- Understand the events during week 1 of development (Zygote, Blastomeres, Morula, Blastocyst)
- Understand the events during week 2 of development (Trophoblast, Syncytiotrophoblast, Cytotrophoblast, Embryoblast, Implantation)
- Brief understanding of early placentation
- Brief understanding of maternal changes
Lecture Resources
Movies | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
| |||||||||||||
|
|
|
| ||||||||||||
|
| ||||||||||||||
Week 2 | |||||||||||||||
|
|
|
References | |||
---|---|---|---|
Hill, M.A. (2020). UNSW Embryology (20th ed.) Retrieved June 16, 2024, from https://embryology.med.unsw.edu.au |
| ||
Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders. | The following chapter links only work with a UNSW connection. | Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone. | The following chapter links only work with a UNSW connection.
|
Take the Week 1 and 2 Quiz (this is not the 2018 assessment quiz that will be held in the practical class).
Fertilization
|
|
Fertilization - Spermatozoa
- Sperm Binding - zona pellucida protein ZP3 acts as receptor for sperm
- Acrosome Reaction - exyocytosis of acrosome contents (Calcium mediated) MBoC - Figure 20-31. The acrosome reaction that occurs when a mammalian sperm fertilizes an egg
- enzymes to digest the zona pellucida, exposes sperm surface proteins to bind ZP2
- Membrane Fusion - between spermatozoa and oocyte, allows spermatozoa nuclei passage into oocyte cytoplasm
Fertilization- Oocyte
- Membrane Depolarization - caused by sperm membrane fusion, primary block to polyspermy
- Cortical Reaction - IP3 pathway elevates intracellular Calcium, exocytosis of cortical granules MBoC - Figure 20-32. How the cortical reaction in a mouse egg is thought to prevent additional sperm from entering the egg
- enzyme alters ZP3 so it will no longer bind sperm plasma membrane
- Meiosis 2 - completion of 2nd meiotic division
- forms second polar body (a third polar body may be formed by meiotic division of the first polar body)
Zygote Formation
- zygote (Carnegie stage 1) is the first diploid cell formed following fertilisation.
- male and female pronuclei, 2 nuclei approach each other and nuclear membranes break down.
- DNA replicates, first mitotic division
- sperm contributes centriole which organizes mitotic spindle
Pronuclear Fusion and Parental Genomes Movies | |
---|---|
<html5media height="340" width="320">File:Pronuclear_fusion_001.mp4</html5media> | <html5media height="340" width="320">File:Parental_genome_mix_02.mp4</html5media> |
- Conceptus - the term refers to all material derived from this fertilised zygote, includes both the embryo and the non-embryonic tissues (placenta, fetal membranes).
- Links: Fertilization | Carnegie stage 1
Cleavage of Zygote
Zygote Division Movie |
---|
<html5media height="400" width="400">File:Mouse_zygote_division.mp4</html5media>
Click Here to play on mobile device | Mouse Zygote Movie page |
Human Zygote to Blastocyst Development (day 1 to 6)
- Links: Carnegie stage 2 |
Morula
Human Embryo (day 2) | Human Embryo (day 3) |
- about day 4 is a solid ball of 16-20 cells with peripheral cells flattened against zona pellucida
- compaction occurs forming a cavity and leading to the next blastocyst stage
Blastocyst
- about day 5 have 2 identifiable cell types and a fluid-filled cavity (blastoceol)
- outer cell layer - trophoblast, peripheral flattened cells, forms the placenta and placental membranes
- inner cell mass - embryoblast, mass of rounder cells located on one wall of the blastocoel, forms entire embryo
Human Blastocyst Movies |
---|
<html5media height="470" width="500">File:Human_blastocyst_day_3-6.mp4</html5media> |
Blastula Cell Communication
Two forms of cellular junctions
- tight junctions, close to outer surface create a seal, isolates interior of embryo from external medium
- gap junctions, allow electrically couple cells of epithelium surrounding a fluid-filled cavity
Tight junctions | Gap junctions |
Blastocyst Hatching
Human Blastocyst Hatching Movie |
---|
<html5media height="470" width="500">File:Human_blastocyst_hatching_day_5-6.mp4</html5media> |
Blastocyst Hatching - zona pellucida lost, ZP has sperm entry site, and entire ZP broken down by uterine secretions and possibly blastula secretions. Uterine Glands - secretions required for blastocyst motility and nutrition
Week 2 - Implantation
Implantation Movie |
---|
<html5media height="580" width="500">File:Week2_001.mp4</html5media> |
The second week of human development is concerned with the process of implantation and the differentiation of the blastocyst into early embryonic and placental forming structures.
Normal Implantation Sites - in uterine wall superior, posterior, lateral |
|
Endometrial Receptivity
Abnormal Implantation
Ectopic Ultrasound Movie |
---|
<html5media height="550" width="660">File:Ectopic_01.mp4</html5media> |
Abnormal implantation sites or Ectopic Pregnancy occurs if implantation is in uterine tube or outside the uterus.
- sites - external surface of uterus, ovary, bowel, gastrointestinal tract, mesentry, peritoneal wall
- If not spontaneous then, embryo has to be removed surgically
Tubal pregnancy - 94% of ectopic pregnancies
- if uterine epithelium is damaged (scarring, pelvic inflammatory disease)
- if zona pellucida is lost too early, allows premature tubal implantation
- embryo may develop through early stages, can erode through the uterine horn and reattach within the peritoneal cavity
Uterus
Endometrial Layers
- Compact - implantation occurs in this layer, dense stromal cells, uterine gland necks, capillaries of spiral arteries
- Spongy - swollen stromal cells, uterine gland bodies, spiral arteries
- Basal - not lost during menstruation or childbirth, own blood supply
Decidual Reaction
- transformation of endometrial stromal cells
- occurs initially at site of implantation and includes both cellular and matrix changes
- reaction spreads throughout entire uterus, not at cervix
- deposition of fibrinoid and glycogen and epithelial plaque formation (at anchoring villi)
- presence of decidual cells are indicative of pregnancy
Other Uterine Changes
- Cervix - at mouth of uterus, secretes mucus (CMP), forms a plug/barrier, mechanical and antibacterial
- Vascular - increased number of blood vessels
Decidua
The endometrium becomes the decidua and forms 3 distinct anatomical regions (at approx 3 weeks)
- Decidua Basalis at implantation site
- Decidua Capsularis enclosing the conceptus
- Decidua Parietalis the remainder of uterus
- Decidua Capsularis and Parietalis fuse eventually fuse and uterine cavity is lost by 12 weeks
Uterus Abnormalities
Endometriosis endometrial tissue located in other regions of the uterus or other tissues. This misplaced tissue develops into growths or lesions which respond to the menstrual cycle hormonal changes in the same way that the tissue of the uterine lining does; each month the tissue builds up, breaks down, and sheds.
Conceptus
Bilaminar Embryoblast
|
<html5media height="300" width="250">File:Chorion 001.mp4</html5media> |
Bilaminar Trophoblast
Two trophoblast layers Cytotrophoblast and Syncitiotrophoblast.
Cytotrophoblasts - form a continuous cellular layer that covers the developing placental villi.
Syncitiotrophoblasts
- secrete proteolytic enzymes, enzymes break down extracellular matrix around cells
- Allow passage of blastocyst into endometrial wall, totally surround the blastocyst
- generate spaces that fill with maternal blood- lacunae
- secrete Human Chorionic Gonadotropin (hCG), hormone, maintains decidua and Corpus Luteum, basis of pregnancy diagnostic test, present in urine is diagnostic of pregnancy
- levels peak at 8 to 10 weeks of pregnancy, then decline and are lower for rest of pregnancy
- 1-2 months: 5,000-200,000 mIU/ml; Non-pregnant females: <5.0 mIU/ml; Postmenopausal females: <9.5 mIU/ml)
- Later in development placenta will secrete hCG
Human ovary corpus luteum | Trophoblast hCG | Pregnancy Test Kit |
Twinning
Twinning can be due to two separate fertilization events (dizygotic twins) or as an abnormality of a single fertilization (monozygotic twins) event during the early weeks of development.
Dizygotic Twinning
Dizygotic twins (fraternal, non-identical) arise from separate fertilization events involving two separate oocyte (egg, ova) and spermatozoa (sperm).
- In dizygotic twinning the genetic material is different and implantation and placentation is also different.
Monozygotic Twinning
- In monozygotic twinning the genetic material is initially identical and degree of twinning will depend upon the timing (early to late) from separate fetal membranes and placenta to conjoined twins.
- morula stage (diamniotic dichorionic), early blastocyst (diamniotic monochorionic), late blastocyst to bilaminar (monoamniotic monochorionic), bilaminar to trilaminar embryo (conjoined)
- Monozygotic twins are a unique research resource for comparing environmental effects on development and health.
- Congenital abnormality statistics for twins is generally increased in various conditions.
Monoygotic twins (identical) produced from a single fertilization event (one fertilised egg and a single spermatazoa, form a single zygote), these twins therefore share the same genetic makeup. Occurs in approximately 3-5 per 1000 pregnancies, more commonly with aged mothers. The later the twinning event, the less common are initially separate placental membranes and finally resulting in conjoined twins.
Week | Week 1 | Week 2 | |||||||||||||
Day | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
Cell Number | 1 | 1 | 2 | 16 | 32 | 128 | bilaminar | ||||||||
Event | Ovulation | fertilization | First cell division | Morula | Early blastocyst | Late blastocyst
Hatching |
Implantation starts | X inactivation | |||||||
Monoygotic
Twin Type |
Diamniotic
Dichorionic |
Diamniotic
Monochorionic |
Monoamniotic
Monochorionic |
Conjoined | |||||||||||
Table based upon recent Twinning Review.[1]
- ↑ <pubmed>12957099</pubmed>
- Links: Twinning | Australian Twin Registry
Now watch the Week 1 overview.
Week 1 Movie |
---|
<html5media height="260" width="660">File:Week1_001.mp4</html5media> |